It is known that organic materials are damaged by light, radiation, heat or oxygen. There are already numerous documents which describe compounds for stabilizing organic material against these effects. The majority of such compounds are free-radical scavengers, hydroperoxide destroyers, quenchers (extinguishers for excited states) or UV absorbers (cf. R. Gachter, H. Muller, Plastics Additives Handbook, 3rd Ed., Hanser Verlag, Munich 1990, p. 133 ff.). In the context of UV absorbers, the compounds generally involved are based on 2-hydroxybenzophenone, 2-hydroxyphenyl-benzotriazole, cinnamic esters and oxanilides (cf. R. Gachter, H. Muller, Plastics Additives Handbook, 3rd Ed., Hanser Verlag, Munich 1990, p. 181 ff.). The class of the o-hydroxy-substituted triphenylpyrimidines can be regarded as a relatively new type of UV stabilizer (DE-A-4416809).
Said classes of compound often have specific disadvantages which occur alongside the desired stabilizing effect. Especially in respect of color behavior, interaction with pigments, compatibility of different, simultaneously employed stabilizers with one another and with the material to be stabilized, resistance to chemicals and water (sensitivity to hydrolysis), storage stability, migration behavior and improvement of stabilization against the damaging effects of heat and light in long-term use, there is a great need for new classes of stabilizer.
Derivatives of 4-hydroxyquinoline-3-carboxylic acid, especially the free acid and the methyl and ethyl esters, have been known for some time in connection with pharmaceutical applications (cf. e.g. B. E. Schroetter et al, Pharmazie (1977), 32(4), 223-5).
The applications known to date relate to the action of 4-hydroxyquinoline-3-carboxylic acid and its esters against bacteria, parasites, tumors, suppurating ulcers, gastrointestinal dysfunctions and as enzyme inhibitors. Derivatives of 4-hydroxyquinoline-3-carboxylic acid are not known for their UV-stabilizing action. Substances which combine a UV stabilizer and a sterically hindered amine simultaneously in the molecule can be particularly effective light stabilizers. In this context, for example, UV absorbers based on 2-hydroxy-benzophenone, on 2-hydroxyphenylbenzotriazole and on cinnamic acids are encountered. This is known, inter alia, from EP-A-389 427; EP-A-10 516; EP-A-16 723; EP-A-200 190; EP-A-593 936; DE-A-4 327 297.